Microcrystalline cellulose particle supported sol-gel sorbents

ABSTRACT

Solid phase extraction (SPE) sorbents and liquid chromatography (LC) stationary phases are provided, as well as methods of fabricating the same. The SPE sorbents and LC stationary phases can use microcrystalline cellulose particles as the substrate and sol-gel sorbent coating technology as the polymer/sorbent immobilization technology. The SPE sorbents and LC stationary phases are stable in a pH range of 1-13 and at a temperature of up to 350 ° C.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Ser. No.16/913,222, filed Jun. 26, 2020, the disclosure of which is herebyincorporated by reference in its entirety, including all figures,tables, and drawings.

BACKGROUND

Porous silica particles are the predominant substrates used in liquidphase separation as the support for the chromatographic stationaryphases and in sample preparation as the support for solid phaseextraction sorbents. More than 90% of liquid phase stationary phases arebased on silica substrates. Although silica particles are universallyaccepted as an ideal support for chromatographic stationary phases dueto their good mechanical strength, high surface area, and reasonablechemical and thermal stability, silica based liquid chromatography (LC)stationary phases suffer from shortcomings, including limited pHstability (maximum stable pH range of 2-9), low maximum operatingtemperature (about 60° C.), and high concentration of surface silanolgroups due to the incomplete derivatization. Silica supported LCstationary phases often suffer from broad and tailing peaks, increasedretention, column-to-column irreproducibility, peak shapeirreproducibility especially for basic compounds, and substantiallydifferent retention and selectivity parameter of the same phase obtainedfrom different manufacturers.

The silica surface contains both silanols (Si—OH) and siloxanes(Si—O—Si) bonds as shown in FIG. 1. Silanol groups are strong adsorptionsites, and silanols present on the surface are used to connect alkylgroups (e.g., C8, C18) in the bonded phases. However, due to sterichindrance, many silanol groups are not readily accessible and can't belinked to alkyl groups. As a result, some of the silanol groups remainunreacted, and these unreacted silanol groups are weakly acidic and posegreat challenges for analyzing basic compounds.

Another major shortcoming of silica based LC stationary phases is poorpH stability. An acidic sample matrix with pH value lower than 2 makesthe surface bonded organic ligands susceptible to chemical damage due tothe hydrolysis of the siloxane bonds that anchor them to the silicasurface. On the other hand, the silica backbone begins to dissolve at apH of greater than 8. Basic compounds such as amines may require pHadjustment to a higher value so that they remain undissociated tofacilitate their extraction/chromatographic separation as neutralentities. Due to the absence of high pH stable LC stationary phase,derivatization of both acidic and basic compounds is commonly used.

Yet another major shortcoming of silica based LC stationary phases islow thermal stability. A majority of popular LC stationary phases suchas C18 offer stable chromatographic performance up to 60° C. At highertemperatures, the silica backbone tends to dissolve at a faster andunsustainable rate. Temperature is an important parameter that can beeffectively utilized to modify the selectivity parameter of the LCstationary phase, to reduce the analysis time, to enhance columnefficiency, and to improve detection sensitivity. However, due to theabsence of LC stationary phases capable of withstanding hightemperature, the potential advantages of this unique parameter largelyremained untapped.

BRIEF SUMMARY

Embodiments of the subject invention provide novel and advantageoussolid phase extraction (SPE) sorbents and liquid chromatography (LC)stationary phases and methods of fabricating the same. The SPE sorbentsand LC stationary phases can use microcrystalline cellulose particles asthe substrate and sol-gel sorbent coating technology as thepolymer/sorbent immobilization technology. The incorporation ofmicrocrystalline cellulose particles and sol-gel sorbent coatingtechnology provides SPE sorbents and LC stationary phases withsubstantially expanded pH stability (stable in pH range of 1-13) andhigh thermal stability (stable up to a temperature of 350° C. or evenhigher). Due to the elimination of acidic Si—OH bonds that would bepresent on a silica substrate, the SPE sorbents and LC stationary phasesare not prone to adsorb basic compounds (e.g., amines), which is whathappens in silica based LC stationary phases. The SPE sorbents and LCstationary phases overcome the shortcomings of conventional LCstationary phases (low pH stability, low thermal stability, wideselectivity variation due to the different content of residual surfacesilanol group, multistep synthesis and derivatization process), and theyalso make high temperature liquid chromatography (HTLC) more realistic,in which water on its own (i.e., only water) can be used as the mobilephase; the dielectric constant of water at 225° C. is comparable to thatof acetonitrile at room temperature.

In an embodiment, a method of fabricating an SPE sorbent or LCstationary phase can comprise: activating microcrystalline celluloseparticles by treatment with a solution; preparing a sol solution bydissolving a polymer in a solvent with an acidic sol-gel catalyst; andadding the activated microcrystalline cellulose particles to the solsolution such that the SPE sorbent or LC stationary phase is formed withthe microcrystalline cellulose particles as a substrate. The method canfurther comprise: cleaning the activated microcrystalline celluloseparticles and drying the cleaned activated microcrystalline celluloseparticles prior to adding to the sol solution; and/or cleaning the SPEsorbent or LC stationary phase. The polymer can be, for example,octadecyl trimethoxysilane, polydimethyldiphenylsiloxane, polyethyleneglycol, polytetrahydrofuran, (p-methyl phenyl) methyldimethoxysilane,3,4-methylenedioxyphenyltriethoxysilane, hydroxyterminated poly(dimethylsiloxane), or monohydroxyterminated poly(dimethylsiloxane). Thepreparing of the sol solution can comprise dissolving the polymer in thesolvent with the acidic sol-gel catalyst and a cross-linker.

In another embodiment, a composition can comprise: a substratecomprising microcrystalline cellulose particles; and a sol-gel sorbentcoated on the substrate. The composition is stable in a pH range of 1-13and at a temperature of 350° C. The sol-gel sorbent can be a polymer.The sol-gel sorbent can comprise, for example, octadecyltrimethoxysilane, polydimethyldiphenylsiloxane, polyethylene glycol,polytetrahydrofuran, (p-methyl phenyl) methyldimethoxysilane,3,4-methylenedioxyphenyltriethoxysilane, hydroxyterminated poly(dimethylsiloxane), or monohydroxyterminated poly(dimethylsiloxane).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing different types of surface silanol(Si-OH) functional groups present on silica particles.

FIG. 2(a) is a chromatogram of caffeine derivatives (1. hypoxanthine; 2.theobromine; 3. theophylline; 4. Caffeine; 5.β-hydroxy-ethyl-theophylline) on a ZirChrom-DB-C18 column (50×4.6 mm id)with UV detection at 254 nm, using 60% water-40% methanol at 25° C., 1milliliter per minute (mL/min). This figure is from Yang (Subcriticalwater chromatography: A green approach to high-temperature liquidchromatography, Journal of Separation Science, 30 (2007) 1131-1140)

FIG. 2(b) is a chromatogram of caffeine derivatives (1. hypoxanthine; 2.theobromine; 3. theophylline; 4. Caffeine; 5.β-hydroxy-ethyl-theophylline) on a ZirChrom-DB-C18 column (50×4.6 mm id)with UV detection at 254 nm, using water at 150° C., 7 mL/min. Thisfigure is from Yang (supra.).

FIG. 3 is a schematic view showing the chemical structure of a cellulosesubstrate, demonstrating available hydroxyl functional groups foranchoring a sol-gel inorganic-organic network, according to anembodiment of the subject invention.

FIG. 4(a) is a chemical reaction involved in acid catalyzed sol-gelcellulose sorbents and liquid chromatographic stationary phases,according to an embodiment of the subject invention.

FIG. 4(b) is a chemical reaction involved in acid catalyzed sol-gelcellulose sorbents and liquid chromatographic stationary phases,according to an embodiment of the subject invention.

FIG. 4(c) is a chemical reaction involved in acid catalyzed sol-gelcellulose sorbents and liquid chromatographic stationary phases,according to an embodiment of the subject invention;polydimethyldiphenylsiloxane is shown here as an example.

FIG. 4(d) is a chemical reaction involved in acid catalyzed sol-gelcellulose sorbents and liquid chromatographic stationary phases,according to an embodiment of the subject invention.

FIG. 5(a) is a chemical reaction involved in acid-base dual catalyzedsol-gel cellulose sorbents and liquid chromatographic stationary phases,according to an embodiment of the subj ect invention.

FIG. 5(b) is a chemical reaction involved in acid-base dual catalyzedsol-gel cellulose sorbents and liquid chromatographic stationary phases,according to an embodiment of the subj ect invention.

FIG. 5(c) is a chemical reaction involved in acid-base dual catalyzedsol-gel cellulose sorbents and liquid chromatographic stationary phases,according to an embodiment of the subject invention;polydimethyldiphenylsiloxane is shown here as an example.

FIG. 5(d) is a chemical reaction involved in acid-base dual catalyzedsol-gel cellulose sorbents and liquid chromatographic stationary phases,according to an embodiment of the subj ect invention.

FIG. 6 is a schematic view of sol-gel C18 coated cellulose particles,according to an embodiment of the subject invention.

FIG. 7 is a schematic view of sol-gel poly(dimethyldiphenylsiloxane)coated cellulose particles, according to an embodiment of the subjectinvention.

FIG. 8 is a schematic view of sol-gel poly(ethylene glycol) coatedcellulose particles, according to an embodiment of the subjectinvention.

FIG. 9 is a schematic view of sol-gel poly(tetrahydrofuran) coatedcellulose particles, according to an embodiment of the subjectinvention.

FIG. 10 is a schematic view of sol-gel cation exchanging sorbent coatedon cellulose particles, according to an embodiment of the subjectinvention.

FIG. 11 is a schematic view of sol-gel mixed mode sorbent coated oncellulose particles (neutral and cation exchanging), according to anembodiment of the subject invention.

FIG. 12 is a schematic view of sol-gel anion exchanging sorbent coatedon cellulose particles, according to an embodiment of the subjectinvention.

FIG. 13 is a schematic view of sol-gel mixed mode sorbent coated oncellulose particles (neutral and anion exchanging), according to anembodiment of the subject invention.

FIG. 14 is a table showing a list of test compounds, along with themolar mass, polarity, and chemical structures of the test compounds.

FIG. 15 is a bar chart showing a comparison of pH stability betweensol-gel cellulose C18, sol-gel cellulose C18 after exposing to pH 1 for24 hours, and sol-gel cellulose C18 after exposing to pH 13 for 24hours. The data in the rows shown under the x-axis are representedrespectively in the bar chart, where the first row is the front bar foreach sorbent, the second row is the second bar from the front for eachsorbent, and so on. It is noted that commercial C18 were found totallydissolved when exposed to pH 13 for 12 hours and substantially dissolvedwhen exposed to pH 1 for 12 hours.

FIG. 16 is a bar chart showing impact of conditioning temperature onacid-base dual catalyzed sol-gel poly(dimethyldiphenylsiloxane) sorbentcoated microcrystalline cellulose particles. The data in the rows shownunder the x-axis are represented respectively in the bar chart, wherethe first row is the front bar for each sorbent, the second row is thesecond bar from the front for each sorbent, and so on.

FIG. 17 is a bar chart showing impact of conditioning temperature onacid-base dual catalyzed sol-gel C18 sorbent coated microcrystallinecellulose particles. The data in the rows shown under the x-axis arerepresented respectively in the bar chart, where the first row is thefront bar for each sorbent, the second row is the second bar from thefront for each sorbent, and so on.

FIG. 18 is a bar chart showing impact of conditioning temperature onacid-base dual catalyzed sol-gel poly(ethylene glycol) sorbent coatedmicrocrystalline cellulose particles. The data in the rows shown underthe x-axis are represented respectively in the bar chart, where thefirst row is the front bar for each sorbent, the second row is thesecond bar from the front for each sorbent, and so on.

FIG. 19 is a bar chart showing impact of conditioning temperature onacid-base dual catalyzed sol-gel poly(tetrahydrofuran) sorbent coatedmicrocrystalline cellulose particles. The data in the rows shown underthe x-axis are represented respectively in the bar chart, where thefirst row is the front bar for each sorbent, the second row is thesecond bar from the front for each sorbent, and so on.

FIG. 20 is a bar chart showing impact of conditioning temperature onacid-catalyzed sol-gel poly(dimethyldiphenylsiloxane) sorbent coatedmicrocrystalline cellulose particles. The data in the rows shown underthe x-axis are represented respectively in the bar chart, where thefirst row is the front bar for each sorbent, the second row is thesecond bar from the front for each sorbent, and so on.

FIG. 21 is a bar chart showing impact of conditioning temperature onacid-catalyzed sol-gel C18 sorbent coated microcrystalline celluloseparticles. The data in the rows shown under the x-axis are representedrespectively in the bar chart, where the first row is the front bar foreach sorbent, the second row is the second bar from the front for eachsorbent, and so on.

FIG. 22 is a bar chart showing impact of conditioning temperature onacid-catalyzed sol-gel poly(ethylene glycol) sorbent coatedmicrocrystalline cellulose particles. The data in the rows shown underthe x-axis are represented respectively in the bar chart, where thefirst row is the front bar for each sorbent, the second row is thesecond bar from the front for each sorbent, and so on.

FIG. 23 is a bar chart showing impact of conditioning temperature onacid-catalyzed sol-gel poly(tetrahydrofuran) sorbent coatedmicrocrystalline cellulose particles. The data in the rows shown underthe x-axis are represented respectively in the bar chart, where thefirst row is the front bar for each sorbent, the second row is thesecond bar from the front for each sorbent, and so on.

FIG. 24 is a bar chart showing a comparison of extraction efficiencyvalues (%, absolute recovery) between acid-catalyzed and acid-base dualcatalyzed sol-gel cellulose sorbents (ABC refers to acid-base dualcatalyzed, and AC refers to acid-catalyzed). The data in the rows shownunder the x-axis are represented respectively in the bar chart, wherethe first row is the front bar for each sorbent, the second row is thesecond bar from the front for each sorbent, and so on.

FIG. 25 is a bar chart showing a comparison of extraction efficiencyvalues (%, absolute recovery) between commercial C18 and sol-gel silicaC18 (acid-base dual catalyzed). The data in the rows shown under thex-axis are represented respectively in the bar chart, where the firstrow is the front bar for each sorbent, the second row is the second barfrom the front for each sorbent, and so on.

FIG. 26 is a bar chart showing a comparison of extraction efficiencyvalues (%, absolute recovery) between commercial C18 and sol-gel silicaC18 (acid-catalyzed). The data in the rows shown under the x-axis arerepresented respectively in the bar chart, where the first row is thefront bar for each sorbent, the second row is the second bar from thefront for each sorbent, and so on.

FIG. 27 is a bar chart showing a comparison of extraction efficiencyvalues (%, absolute recovery) between commercial C18, sol-gel celluloseC18, sol-gel cellulose poly(dimethyldiphenylsiloxane), sol-gel cellulosepoly(ethylene glycol), and sol-gel cellulose poly(tetrahydrofuran). Thedata in the rows shown under the x-axis are represented respectively inthe bar chart, where the first row is the front bar for each sorbent,the second row is the second bar from the front for each sorbent, and soon.

FIG. 28 is a bar chart showing a comparison of Si, O, C loading betweencellulose particles, commercial C18, and microcrystalline cellulosesupported different sol-gel sorbents and stationary phases. The data inthe rows shown under the x-axis are represented respectively in the barchart, where the first row is the front bar for each sorbent, the secondrow is the second bar from the front for each sorbent, and so on.

FIG. 29(a) shows the chemical structure for (p-methyl phenyl)methyldimethoxysilane, a bi-alkoxy silane).

FIG. 29(b) shows the chemical structure for3,4-methylenedioxyphenyltriethoxysilane, a trialkoxy silane.

FIG. 29(c) shows the chemical structure for hydroxyterminatedpoly(dimethyl siloxane), a bihydroxy terminated polymer.

FIG. 29(d) shows the chemical structure for monohydroxyterminatedpoly(dimethylsiloxane).

DETAILED DESCRIPTION

Embodiments of the subject invention provide novel and advantageoussolid phase extraction (SPE) sorbents (or sol-gel sorbents) and liquidchromatography (LC) stationary phases and methods of fabricating thesame. The SPE sorbents and LC stationary phases can use microcrystallinecellulose particles as the substrate and sol-gel sorbent coatingtechnology as the polymer/sorbent immobilization technology. Theincorporation of microcrystalline cellulose particles and sol-gelsorbent coating technology provides SPE sorbents and LC stationaryphases with substantially expanded pH stability (stable in pH range of1-13) and high thermal stability (stable up to a temperature of 350° C.or even higher). Due to the elimination of acidic Si—OH bonds that wouldbe present on a silica substrate, the SPE sorbents and LC stationaryphases are not prone to adsorb basic compounds (e.g., amines), which iswhat happens in silica based LC stationary phases. The SPE sorbents andLC stationary phases overcome the shortcomings of conventional LCstationary phases (low pH stability, low thermal stability, wideselectivity variation due to the different content of residual surfacesilanol group, multistep synthesis and derivatization process), and theyalso make high temperature liquid chromatography (HTLC) more realistic,in which water on its own (i.e., only water) can be used as the mobilephase; the dielectric constant of water at 225° C. is comparable to thatof acetonitrile at room temperature. Embodiments of the subjectinvention can replace related art SPE sorbents and LC stationary phasesand methods of fabricating the same. It is also noted that HTLC couldlead to elimination of expensive, toxic, and environment-pollutingorganic modifiers (methanol, acetonitrile) by using 100% water as themobile phase.

In related art LC separation, water is used mixed with organicmodifier(s) (e.g., methanol, acetonitrile) as the mobile phase. Theusage of organic solvent as the mobile phase modifier incurs high costfor the chromatographic separation as well as significantly high costfor waste disposal. The organic solvent usage in liquid phase separationcan be substantially reduced or even eliminated if water is used at hightemperature and pressure (subcritical water). If the temperature of thewater is increased from 25° C. to 250° C., the polarity, surface tensionand viscosity becomes identical to the aqueous-organic mobile phase(water+ ccetonitrile/methanol) at room temperature. FIGS. 2(a) and 2(b)illustrates the advantage of high temperature liquid chromatography(HTLC). Using the same LC stationary phase (zirconia-C18), superiorseparation and substantially faster separation (in 1 min vs. 7 min) wasachieved using water as the only mobile phase (FIG. 2(b)).

In an embodiment, sol-gel sorbents or LC stationary phases can beacid-catalyzed using a microcrystalline cellulose support. Preparationof acid-catalyzed microcrystalline cellulose supported sol-gel sorbentsand LC stationary phases can comprise the following steps: (a1) surfacecleaning and activation of cellulose particles; (b1) preparation of thesol solution; and (c1) sol-gel sorbent coating process. The process canfurther comprise (d1) conditioning and cleaning of sol-gel sorbentcoated cellulose particles. FIGS. 4(a)-4(d) show chemical reactions thattake place in the acid-catalyzed process for fabricatingmicrocrystalline cellulose supported sol-gel sorbents and LC stationaryphases. Both hydrolysis and polycondensation reactions proceedsimultaneously, resulting in a thin layer of sol-gel sorbent chemicallybonded to the microcrystalline cellulose particles.

The surface cleaning and activation of cellulose particles (step (a1))will now be described in more detail. Microcrystalline celluloseparticles possess abundant surface hydroxyl groups. FIG. 3 shows aschematic view of the chemical structure of cellulose, which is ahydrophilic linear polymer of β-D-glucopyranose. Referring to FIG. 3,each dimer of cellulose contains three hydroxyl functional groups inpositions 2, 3, and 6 that can participate in polycondensation duringthe sol-gel coating process at a varying degree of reactivity. As such,microcrystalline cellulose particles serve as an excellent substrate forsol-gel sorbent coating.

The microcrystalline cellulose particles can be activated (e.g., bytreatment with a solution (e.g., a basic solution such as ammoniumhydroxide or a 1 M NaOH solution) under sonication). Swelling ofcellulose, also known as mercerization, is an important treatment thatimproves its chemical reactivity and significantly increases theavailability of all the hydroxyl groups for chemical reactions. Theactivation can also lead to mercerization. The treated microcrystallinecellulose particles can then washed (e.g., several times with deionizedwater), followed by treatment with a solution (e.g., an acidic solutionsuch as 0.1 M HCl solution, trifluoroacetic acid, nitric acid, aceticacid, or formic acid) under sonication). The treated particles can thenwashed again (e.g., with a large amount of deionized water) and thendried (such as in a drying chamber with a flow of inert gas such ashelium gas). If desired, the dried particles can be stored (e.g., in oneor more airtight containers) until the coating process (step (c1)).

The preparation of the sol solution (step (b1)) will now be described inmore detail. The sol solution for creating microcrystalline cellulosesupported sol-gel sorbents and stationary phases can be prepared bydissolving a polymer (e.g., octadecyl trimethoxysilane,polydimethyldiphenylsiloxane, polyethylene glycol, polytetrahydrofuran,or any ligand connected to bialkoxysilane or trialkoxysilane or anorganic/organic-inorganic polymer with a hydroxyl terminal group), across-linker (e.g., methyltrimethoxysilane (MTMS), ethyltrimethoxysilane, or propyl trimethoxy silane), at least one solvent(e.g., an organic solvent such as methylene chloride : acetone (50:50v/v), methanol, tetrahydrofuran, propanol, or ethanol), and a sol-gelcatalyst (e.g., trifluoroacetic acid (5% water), formic acid, HCl,acetic acid, or oxalic acid). The mixture can be vortexed and/orcentrifuged, and the clear supernatant of the sol solution can then betransferred to a container (e.g., a reaction bottle). Non-limitingexamples of the polymer (precursor) that can be used are shown in FIGS.29(a)-29(d)-(p-methyl phenyl) methyldimethoxysilane (an example of abi-alkoxy silane), 3,4-methylenedioxyphenyltriethoxysilane (an exampleof a trialkoxy silane), hydroxyterminated poly(dimethyl siloxane) (anexample of a bihydroxy terminated polymer), and monohydroxyterminatedpoly(dimethylsiloxane).

The sol-gel sorbent coating process (step (c1)) will now be described inmore detail. Chemically treated microcrystalline cellulose particleswere used as the substrate (see step (a1)). The microcrystallinecellulose particles can be gently inserted into the container having thesol solution so that a three-dimensional network of sol-gel sorbents canbe formed on the surface of the substrate as well as throughout theporous matrix. The microcrystalline cellulose particles can be keptinside the sol solution for a period of time (e.g., 24 hours). Thesol-gel sorbent coating process can be carried out at a temperatureabove room temperature (e.g., inside an oven at 50° C. or more).

The conditioning and cleaning of sol-gel sorbent coated celluloseparticles (step (d1)) will now be described in detail. After completingthe coating, the sol solution can be removed from the container and thesol-gel sorbent coated microcrystalline cellulose particles can be driedand aged (e.g., in a conditioning device inside a gas chromatographyoven), optionally with continuous flow of inert gas (e.g., helium gasflow at 50° C. or more). Before using for extraction, the sol-gelsorbents coated microcrystalline cellulose particles can be rinsed(e.g., sequentially with two different solvents) followed by drying(e.g., at 50° C. under an inert atmosphere). If desired, they can bestored in a closed container to inhibit contamination.

In an embodiment, sol-gel sorbents or LC stationary phases can beacid-base dual catalyzed using a microcrystalline cellulose support.Preparation of acid-base dual catalyzed microcrystalline cellulosesupported sol-gel sorbents and LC stationary phases can comprise thefollowing steps: (a2) surface cleaning and activation of celluloseparticles; (b2) preparation of the sol solution; and (c2) sol-gelsorbent coating process. The process can further comprise (d2)conditioning and cleaning of sol-gel sorbent coated cellulose particles.FIGS. 5(a)-5(d) show chemical reactions that take place in the acid-basedual catalyzed process for fabricating microcrystalline cellulosesupported sol-gel sorbents and LC stationary phases. The sol-gelreactions are carried out in two steps: (1) hydrolysis (e.g., hydrolysisof tetramethylorthosilicate (TMOS)) under acid catalyst; and (b)polycondensation under basic catalyst. A solid gel is formed duringpolycondensation with the encapsulated and chemically bondedmicrocrystalline cellulose particles into its core.

The surface cleaning and activation of cellulose particles (step (a2))is the same as for step (a1) described above. The preparation of the solsolution (step (b2)) will now be described in more detail. The solsolution for creating microcrystalline cellulose supported sol-gelsorbents and stationary phases can be prepared by dissolving a polymer(e.g., octadecyl trimethoxysilane, polydimethyldiphenylsiloxane,polyethylene glycol, polytetrahydrofuran, or any ligand connected tobialkoxysilane or trialkoxysilane or an organic/organic-inorganicpolymer with a hydroxyl terminal group), a cross-linker (e.g., TMOS,MTMS, ethyl trimethoxysilane (ETMOS), or propyl trimethoxy silane(PTMOS)), at least one solvent (e.g., an organic solvent such as2-propanol, methanol, tetrahydrofuran, propanol, ethanol, or a mixturesuch as methylene chloride and acetone (50:50 v/v)), and a sol-gelcatalyst (e.g., HCl (0.1 M), formic acid, trifluoroacetic acid, aceticacid, or oxalic acid). The mixture can be vortexed and/or centrifuged,and the clear supernatant of the sol solution can then be transferred toa container (e.g., a reaction bottle). The mixture can then be heatedfor hydrolysis of the sol-gel precursor(s) (e.g., heated in an oven at50° C. or more for several hours). Non-limiting examples of the polymer(precursor) that can be used are shown in FIGS. 29(a)-29(d)-(p-methylphenyl) methyldimethoxysilane (an example of a bi-alkoxy silane),3,4-methylenedioxyphenyltriethoxysilane (an example of a trialkoxysilane), hydroxyterminated poly(dimethyl siloxane) (an example of abihydroxy terminated polymer), and monohydroxyterminatedpoly(dimethylsiloxane).

The sol-gel sorbent coating process (step (c2)) will now be described inmore detail. Chemically treated microcrystalline cellulose particleswere used as the substrate (see step (a1/a2)). The microcrystallinecellulose particles can be gently inserted into the container having thesol solution under magnetic stirring so that the microcrystallinecellulose particles remain homogeneously dispersed into the solsolution. Subsequently, a base solution (e.g., (1 M NH₄OH, 0.1 M NH₄F,NaOH, or 3-aminopropyl trimethoxysilane) can be added to the solsolution (e.g., added in droplets under vigorous stirring). The solsolution slowly becomes viscous and forms a solid mass after a period oftime (e.g., an hour or about an hour). The solid mass can be heated(e.g., heated in an oven at 50° C. or more for several (e.g., 24)hours).

The conditioning and cleaning of sol-gel sorbent coated celluloseparticles (step (d2)) will now be described in detail. After completingthe conditioning of sol-gel sorbent coated microcrystalline particles,the solid mass can be crushed into small pieces and subsequently cleaned(e.g., in a Soxhlet extraction system using a solvent such asmethanol:methylene chloride (50:50 v/v) for a period of time such asseveral hours (e.g., 6 hours)). The cleaned mass can be dried (e.g., ina vacuum at 80° C. or more for several hours).

FIGS. 6-13 show schematic views of acid-catalyzed and acid-base dualcatalyzed sol-gel sorbents on microcrystalline cellulose particles,according to embodiments of the subject invention. FIG. 6 shows sol-gelC18 coated cellulose particles; FIG. 7 shows sol-gelpoly(dimethyldiphenylsiloxane) coated cellulose particles; FIG. 8 showssol-gel poly(ethylene glycol) coated cellulose particles; FIG. 9 showssol-gel poly(tetrahydrofuran) coated cellulose particles; FIG. 10 showssol-gel cation exchanging sorbent coated on cellulose particles; FIG. 11shows sol-gel mixed mode sorbent coated on cellulose particles (neutraland cation exchanging); FIG. 12 shows sol-gel anion exchanging sorbentcoated on cellulose particles; and FIG. 13 shows sol-gel mixed modesorbent coated on cellulose particles (neutral and anion exchanging).

Embodiments of the subject invention provide several advantages overrelated SPE sorbents and LC stationary phases and methods of fabricatingthe same. For example, the fabrication methods of embodiments of thesubject invention are simpler than related art multistep synthesisprocesses. Also, replacement of silica with microcrystalline celluloseparticles eliminates the problems related to residual surface silanol(Si—OH) groups that pose a great challenge to the separation andanalysis of organic bases (about 70% of pharmaceutical products areorganic bases). Embodiments of the subject invention also substantiallyexpand the working pH range (1-13) and temperature range (up to 350° C.or even higher) in which the SPE sorbents and LC stationary phases arestable. Embodiments of the subject invention provide equivalent orbetter separation for polar, nonpolar, and medium polar compounds, whencompared to related art silica-based SPE sorbents and LC stationaryphases. New extraction sorbents and LC stationary phases are provided,and the extraordinarily high thermal stability of the new LC stationaryphases make HTLC more feasible, which lead to the application ofsubcritical water as the mobile phase and the elimination of toxic andhazardous organic solvents in the mobile phase. Embodiments of thesubject invention therefore mark a milestone in green analyticalchemistry. SPE sorbents of embodiments of the subject invention canempower wastewater treatment plants (WWTP) to be able to removepersistent and emerging pollutants more effectively, and embodiments canalso substantially reduce the production costs of SPE sorbents and LCstationary phases.

A greater understanding of the embodiments of the subject invention andof their many advantages may be had from the following examples, givenby way of illustration. The following examples are illustrative of someof the methods, applications, embodiments, and variants of the presentinvention. They are, of course, not to be considered as limiting theinvention. Numerous changes and modifications can be made with respectto the invention.

EXAMPLE 1 Acid-Catalyzed Sol-Gel Sorbents and LC Stationary Phases

Acid-catalyzed microcrystalline cellulose supported sol-gel sorbents andLC stationary phases were prepared. The microcrystalline celluloseparticles were activated by treating them with 1 M NaOH solution for 1hour under sonication. The base-treated microcrystalline celluloseparticles were then washed several times with deionized water, followedby treating with 0.1 M HCl solution for 1 hour under sonication. Thetreated particles were then washed with a large amount of deionizedwater and then dried in a home-made drying chamber with continuoushelium gas flow at 50° C. overnight. The dried particles were stored ina clean airtight glass container until the step of coating with sol-gelsorbents.

The sol solution for creating microcrystalline cellulose supportedsol-gel sorbents and LC stationary phases was prepared by dissolving 10g of polymer (octadecyl trimethoxysilane, polydimethyldiphenylsiloxane,polyethylene glycol, and po lytetrahydrofuran, respectively, fordifferent sorbents/stationary phases), 10.0 mL of methyltrimethoxysilane(MTMS), 20 mL of methylene chloride : acetone (50:50 v/v) as the organicsolvent, and 4 mL of trifluoroacetic acid (5% water) as the sol-gelcatalyst. The mixture was then vortexed for 3 minutes, centrifuged for 5minutes, and finally the clear supernatant of the sol solution wastransferred to a clean 60 mL amber-colored glass reaction bottle.

The chemically treated microcrystalline cellulose particles were used asthe substrate for the sol-gel sorbent coatings. 5.0 g of the clean andtreated microcrystalline cellulose particles were gently inserted intothe reaction bottle containing the sol solution so that athree-dimensional network of sol-gel sorbents could be formed on thesurface of the substrate as well as throughout the porous matrix. Themicrocrystalline cellulose particles were kept inside the sol solutionfor 24 hours. The sol-gel sorbent coating process was carried out insidean oven at 50° C.

After completing the coating period, the sol solution was expelled fromthe reaction bottle and the sol-gel sorbent coated microcrystallinecellulose particles were dried and aged in a home-made conditioningdevice built inside a gas chromatography oven with continuous helium gasflow at 50° C. for 24 h. Before using for extraction, the sol-gelsorbents coated microcrystalline cellulose particles were rinsedsequentially with methylene chloride and methanol followed by drying at50° C. under an inert atmosphere for 1 hour and stored in a closed glasscontainer to inhibit contamination.

The result was acid-catalyzed sol-gel C18 coated cellulose particles,sol-gel poly(dimethyldiphenylsiloxane) coated cellulose particles,sol-gel poly(ethylene glycol) coated cellulose particles, and sol-gelpoly(tetrahydrofuran) coated cellulose particles. FIG. 28 shows theelemental composition for these sorbent coated cellulose particles, aswell as those for Example 2, standard cellulose particles, andcommercial C18 (a carbon chain with 18 carbons).

EXAMPLE 2 Acid-Base Dual Catalyzed Sol-Gel Sorbents and LC StationaryPhases

Acid-base dual catalyzed microcrystalline cellulose supported sol-gelsorbents and LC stationary phases were prepared. The microcrystallinecellulose particles were activated by treating them with 1 M NaOHsolution for 1 hour under sonication. The base-treated microcrystallinecellulose particles were then washed several times with deionized water,followed by treating with 0.1 M HCl solution for 1 hour undersonication. The treated particles were then washed with a large amountof deionized water and then dried in a home-made drying chamber withcontinuous helium gas flow at 50° C. overnight. The dried particles werestored in a clean airtight glass container until the step of coatingwith sol-gel sorbents.

The sol solution for creating microcrystalline cellulose supportedsol-gel sorbents and LC stationary phases was prepared by dissolving 1.2g of polymer (octadecyl trimethoxysilane, polydimethyldiphenylsiloxane,polyethylene glycol, and polytetrahydrofuran, respectively, fordifferent sorbents/stationary phases), 4.0 mL of tetramethylorthosilicate (TMOS), 30 mL of 2-propanol as the organic solvent, and1.880 mL of HCl (0.1 M) as the sol-gel catalyst. The mixture was thenvortexed for 3 minutes, centrifuged for 5 minutes, and finally the clearsupernatant of the sol solution was transferred to a wide mouthed glassreaction bottle and kept inside an oven at 50° C. overnight forhydrolysis of the sol-gel precursor(s).

The chemically treated microcrystalline cellulose particles were used asthe substrate for the sol-gel sorbent coatings. 4.0 g of the clean andtreated microcrystalline cellulose particles were gently inserted intothe reaction bottle containing the sol solution under continuousmagnetic stirring so that the microcrystalline cellulose particlesremain homogeneously dispersed into the sol solution. Subsequently, 1 mLof a base solution (1 M NH₄OH, 0.1 M NH₄F) was added to the sol solutionin droplets under vigorous stirring. The sol solution slowly becameviscous and formed a solid mass in an hour. The solid mass was keptinside the oven at 50° C. for 24 hours.

After completing the conditioning of sol-gel sorbent coatedmicrocrystalline particles, the solid mass was crushed into small piecesand subsequently cleaned in a Soxhlet extraction system using methanol :methylene chloride (50:50 v/v) for 6 hours. The cleaned mass was thendried in a vacuum oven overnight at 80° C.

The result was acid-base dual catalyzed sol-gel C18 coated celluloseparticles, sol-gel poly(dimethyldiphenylsiloxane) coated celluloseparticles, sol-gel poly(ethylene glycol) coated cellulose particles, andsol-gel poly(tetrahydrofuran) coated cellulose particles. FIG. 28 showsthe elemental composition for these sorbent coated cellulose particles,as well as those for Example 1, standard cellulose particles, andcommercial C18 (a carbon chain with 18 carbons).

EXAMPLE 3 Study of pH Stability

A study of pH stability of the acid-catalyzed sorbent coated celluloseparticles and the acid-base dual catalyzed sol-gel sorbent coatedcellulose particles was performed, where the sol-gel sorbent coatedcellulose particles were exposed to (a) pH 1 solution for 12 hours atroom temperature, and (b) pH 13 solution for at room temperature for 12hours. In each case, subsequently, the cellulose particles were rinsedwith a large amount of deionized water several times. The particles werethen dried in a vacuum oven at 80° C. for 24 hours. The treatedparticles were then stored in air-tight plastic containers until theirapplication.

FIG. 15 shows the results, demonstrating that the acid-catalyzed sorbentcoated cellulose particles and the acid-base dual catalyzed sol-gelsorbent coated cellulose particles of embodiments of the subjectinvention are stable at pH=1 and pH=13.

EXAMPLE 4 Study of Temperature Stability

A study of thermal stability of the acid-catalyzed sorbent coatedcellulose particles and the acid-base dual catalyzed sol-gel sorbentcoated cellulose particles was performed, where the sol-gel sorbentcoated cellulose particles were exposed to (a) a temperature of 250° C.for 2 hours; (b) a temperature of 300° C. for 2 hours; and (c) atemperature of 350° C. for 2 hours. The study was carried out in aconditioning device built inside of a gas chromatography oven undercontinuous N₂ gas flow.

FIGS. 16-23 show the results, demonstrating that the acid-catalyzedsorbent coated cellulose particles and the acid-base dual catalyzedsol-gel sorbent coated cellulose particles of embodiments of the subjectinvention are stable at temperatures up to 350° C. or even slightlyhigher).

EXAMPLE 5 Evaluation of Extraction Performance

An evaluation of extraction performance of commercial C18,acid-catalyzed sorbents, and acid-base dual catalyzed sorbents wascarried out by exposing 50 mg of precisely weighed sorbent to 10 mL of a10 μg/mL aqueous solution of the test compounds listed in FIG. 14 for 1hour with continuous magnetic stirring at 1000 revolutions per minute(rpm). The absolute recovery of the sorbents was calculated by analyzingthe original solution and the residual solution after the extraction. %absolute recovery=[(concentration in the original solution—concentrationin the residual solution)/concentration in the original solution]*100%.

FIGS. 24-27 show the results, demonstrating that the acid-catalyzedsorbent coated cellulose particles and the acid-base dual catalyzedsol-gel sorbent coated cellulose particles of embodiments of the subjectinvention have excellent extraction efficiency.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

What is claimed is:
 1. A composition, comprising: a substrate comprisingmicrocrystalline cellulose particles; and a sol-gel sorbent coated onthe substrate, the composition being stable in a pH range of 1-13, andthe composition being stable at a temperature of 350° C.
 2. Thecomposition according to claim 1, the sol-gel sorbent being a polymer.3. The composition according to claim 1, the substrate beingmicrocrystalline cellulose.
 4. The composition according to claim 1, thesubstrate being chemically pre-treated.
 5. The composition according toclaim 1, the substrate being chemically pre-treated with a base and anacid.
 6. The composition according to claim 5, the acid being selectedfrom HCl, trifluoroacetic acid, nitric acid, acetic acid, and formicacid.
 7. The composition according to claim 6, the base being ammoniumhydroxide or NaOH.
 8. The composition according to claim 5, the basebeing ammonium hydroxide or NaOH.
 9. The composition according to claim1, the composition being stable at a temperature greater than 350° C.10. The composition according claim 1, the sol-gel sorbent comprisingC18, poly(dimethyldiphenyl), poly(ethylene glycol), polytetrahydrofuran,(p-methyl phenyl) methyldimethoxysilane,3,4-methylenedioxyphenyltriethoxysilane, hydroxyterminated poly(dimethylsiloxane), or monohydroxyterminated poly(dimethylsiloxane).
 11. Thecomposition according claim 10, the sol-gel sorbent comprising C18. 12.The composition according claim 10, the sol-gel sorbent comprisingpoly(dimethyldiphenyl).
 13. The composition according claim 10, thesol-gel sorbent comprising poly(ethylene glycol).
 14. The compositionaccording claim 10, the sol-gel sorbent comprising polytetrahydrofuran,(p-methyl phenyl) methyldimethoxysilane.
 15. The composition accordingclaim 10, the sol-gel sorbent comprising3,4-methylenedioxyphenyltriethoxysilane.
 16. The composition accordingclaim 10, the sol-gel sorbent comprising hydroxyterminated poly(dimethylsiloxane).
 17. The composition according claim 10, the sol-gel sorbentcomprising monohydroxyterminated poly(dimethylsiloxane).
 18. Acomposition, comprising: a substrate comprising microcrystallinecellulose particles; and a sol-gel sorbent coated on the substrate, thecomposition being stable in a pH range of 1-13, the composition beingstable at a temperature of 350° C. and a temperature greater than 350°C., the sol-gel sorbent being a polymer, the substrate beingmicrocrystalline cellulose, the substrate being chemically pre-treatedwith an acid and a base, and the sol-gel sorbent comprising C18,poly(dimethyldiphenyl), poly(ethylene glycol), polytetrahydrofuran,(p-methyl phenyl) methyldimethoxysilane,3,4-methylenedioxyphenyltriethoxysilane, hydroxyterminated poly(dimethylsiloxane), or monohydroxyterminated poly(dimethylsiloxane).
 19. Thecomposition according to claim 18, the acid being HCl.
 20. Thecomposition according to claim 19, the base being NaOH.